1. Field of the Invention
The present invention relates to ferrite sintered compacts, and particularly relates to a ferrite sintered compact which is preferably used as an element of an electronic part having an internal conductor containing silver. The present invention also relates to an electronic part comprising the ferrite sintered compact.
2. Description of the Related Art
Elements of electronic parts, such as inductor parts, are generally composed of ferrite sintered compacts. Some elements contain internal conductors therein. In this case, a calcination for obtaining ferrite sintered compacts is performed in a state in which internal conductors are formed therein. Silver and silver-palladium alloys are frequently used as conductor components contained in the internal conductors.
In order to produce a ferrite sintered compact satisfying required electrical characteristics, the ferrite must be fired at a relatively high temperature in the sintering step. When an internal conductor containing silver is formed, the silver contained in the internal conductor will be diffused into the ferrite portion during such high-temperature firing. Thus, the resulting electronic part may have deteriorated electrical characteristics.
A possible countermeasure of the above problem is addition of glass to the ferrite. Glass functions as a sintering promoter and decreases the sintering temperature of the ferrite. Thus, a decrease in sintering temperature by addition of glass enables calcination of the ferrite at a relatively low temperature, and thus suppresses diffusion of silver into the ferrite portion.
For example, Japanese Patent Application Laid-Open Nos. 1-110708 and 2-288307 disclose improved sintering characteristics of ferrite and improved mechanical strength and electrical characteristics, by addition of borosilicate glass to the ferrite.
Although the added borosilicate glass surely functions as a sintering promoter and decreases the sintering temperature of the ferrite, it has been found that borosilicate glass accelerates the diffusion of silver. Since boron accelerates diffusion of silver, the borosilicate glass, which is added in an amount of 1 percent by volume or more, further accelerates such tendency.
On the other hand, a large amount of glass effectively contributes to low-temperature sintering of ferrite. Regarding electrical characteristics, ferrite containing several tens percent by volume of glass can effectively suppress distortion of current high-frequency signals. In addition, many preferable effects are expected when a relatively large amount of glass is added.